The invention relates to a coolant circuit for an internal combustion engine, wherein the coolant can circulate between the internal combustion engine and a heat sink as a function of a switchable valve which is closed in the initial state during a cold start of the internal combustion engine, and to a method of operating a coolant circuit.
Such coolant circuits are used in particular in the automotive industry to cool coolant, heated by the internal combustion engine, through circulation via the heat sink. In this way, the internal combustion engine is protected from damage due to overheating. To reduce friction work of the internal combustion engine in terms of improved efficiency, a rapid heating of the internal combustion engine and thus also of the coolant is desirable, when the internal combustion engine is at a cold start. For this reason, a valve switched to a closed state can prevent a coolant circulation until a sufficient heating has been reached.
The determination of the point in time for opening the valve is realized in the art in dependence on when the internal combustion engine exceeds a torque or rotation speed threshold. DE 100 45 613 A1 discloses a method for controlling the coolant temperature of an engine cooling system, with the coolant temperature being controlled in dependence on a load and/or rotation speed of the internal combustion engine. This oftentimes leads to premature opening of the valve, when the coolant temperatures are too low so that efficiency losses have to be accepted.
DE 101 54 091 A1 describes a method and a device for controlling a cooling system of an internal combustion engine, with the capacity of a coolant pump being controllable as a function of a fuel quantity fed to the internal combustion engine. However, the fuel quality is not readily useful as a control variable for controlling a cooling system because of the absence of a stoichiometric conversion of the fuel, in particular during a cold start of the internal combustion engine.